To date, almost all improvements in agricultural crops have been achieved using traditional plant breeding techniques. These techniques involve crossing parental plants with different genetic backgrounds to generate progeny with genetic diversity. The progeny are then selected to obtain those plants that express the desired traits. Desired traits are then fixed while deleterious traits are eliminated via multiple backcrossings or selfings to eventually yield progeny with the desired characteristics. Hybrid corn, low erucic acid oilseed rape, high oil corn, and hard white winter wheat are examples of significant agricultural advances achieved with traditional breeding.
However, the amount of genetic diversity in the germplasm of a particular crop limits what can be accomplished by breeding. Although traditional breeding has proven to be very powerful, as advances in crop yields over the last century demonstrate, recent data suggest that the rate of yield improvement is tapering off for major food crops (Lee (1998) Proc. Natl. Acad. Sci. USA 95: 2001-2004). The introduction of molecular mapping markers into breeding programs may accelerate the process of crop improvement in the near term, but ultimately the lack of new sources of genetic diversity will become limiting. In particular, traditional breeding has proved rather ineffective for improving many polygenic traits such as increased disease resistance.
In recent years, biotechnology approaches involving the expression of single transgene in crops have resulted in the successful commercial introduction of new plant traits, including herbicide resistance (glyphosate or Roundup resistance), insect resistance (expression of Bacillus thuringiensis toxins) and virus resistance (over expression of viral coat proteins). However, the list of single gene traits of significant value is relatively small. The greatest potential of biotechnology lies in engineering complex polygenic traits for environmental stresses, disease, plant development and architecture, yield and quality traits. Presently, engineering such polygenic traits has proven extremely challenging.
The present invention provides a novel method for the rapid identification of genes that are useful for modifying complex plant traits.